Pressure vessel steel plate resistant against hydrogen-induced cracking and manufacturing method thereof

ABSTRACT

An anti-hydrogen-induced-cracking pressure vessel steel plate containing, chemical composition of the steel plate according to the weight percentage: 0.16-0.20% of C, 0.15-0.40% of Si, 1.05-1.20% of Mn, less than or equal to 0.008% of P, less than or equal to 0.002% of S, less than or equal to 0.01% of Nb, less than or equal to 0.01% of V, less than or equal to 0.01% of Ti, less than or equal to 0.0005% of B, and the balance being Fe and inevitable impurity elements; carbon equivalent Ceq is less than or equal to 0.42%, and the computational formula for the carbon equivalent is Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15.

This application is the U.S. national phase of International ApplicationNo. PCT/CN2016/102379 filed on 18 Oct. 2016 which designated the U.S.and claims priority to Chinese Application No. CN201610241719.3 filed on19 Apr. 2016, the entire contents of each of which are herebyincorporated by reference.

TECHNICAL FIELD

The invention belongs to the field of steel plate manufacturing, inparticular to a thickness of 50 mm SA516Gr70 CHIC) pressure vessel steelplate which is resistant to hydrogen induced cracking (HIC), andmanufacturing method thereof.

BACKGROUND

SA516Gr70 (HIC) steel plate is mainly used in petroleum and chemicalequipment used in wet H2S corrosion environment. Hydrogen inducedcracking is a common failure mode in wet hydrogen sulfide environment,H2S reacts with steel surface to generate hydrogen atoms, the hydrogenatoms diffuse into steel and gather at the metallurgical defect positionto generate hydrogen molecules. In this way, high internal stress isgenerated inside steel, resulting in interfacial crack and hydrogenblistering, and when the pressure of hydrogen continues to increase,small hydrogen bubbles tend to connect with each other, forming a ladderlike hydrogen induced cracking

In the wet H2S corrosion environment, the pressure vessel once failedwill pose a serious threat to production safety and bring huge economiclosses. With quality deterioration of resources, and the trend oflarge-scale and light-weight design in equipment, the design requiresthat the steel plate still has good mechanical properties and excellentanti hydrogen cracking (HIC) properties at higher temperatures andlonger simulated post weld heat treatment conditions.

At present, most medium-heavy plate enterprises use the design ofcombination of C, Mn and Si element content, ensure the HIC performanceof steel plate by reducing the C, Mn, S, P content, banded structuregrade and non-metallic inclusion. With the temperature increasing duringsimulated post weld heat treatment and extension of time for simulatedpost weld heat treatment, the tensile strength of the sample aftersimulated welding heat treatment will decrease markedly.

Under the condition of limiting carbon content and microalloying elementcontent, tensile strength is difficult to reach the standardrequirement, especially the mechanical properties of head steel plateafter hot forming often are unable to restore to the standardperformance. To improve the strength of steel plates, the methods,including the forging slab rolling, reducing the content of C, andadding Ni and Cu elements are adopted by some foreign enterprises.Although this method can improve strength of steel plate, but productioncycle is longer and results in higher production cost.

Currently there are few patents related toanti-hydrogen-induced-cracking pressure vessel steel used in wet H2Senvironment. Three heat treatment processes are adopted in general. Theinvention patent CN104480384A adopts the normalizing and air coolingtechnology during production, and subsequent cooling in still air duringproduction. The invention patent CN1046411629A adopts the normalizingand air-spray cooling technology. The invention patent CN102605242Aadopts the quenching and tempering technology. These three thermaltreatment technologies all have a few limitations. Though thenormalizing and air cooling technology is beneficial to form uniformmicrostructure of steel plates, the strength of a sample can hardly meetthe requirement after long-time high-temperature simulated post-weldingheat treatment; By conducting air-spray cooling after normalizing, thebanded structure of steel plates can be improved to a certain extent,but the effect on improving the strength of steel plate is not obvious.Since tempering treatment is not used, a martensitic structure orbainite structure might be generated on the surface of steel plate dueto fast cooling, which leads to low strength and high surface hardnessof steel plate, and eventually leads to edge cracking of steel plate incontainer manufacturing process; The quenching and tempering technologycan remarkably improve the strength of steel plate. However, due to thefact that quenching temperature is high and cooling speed is too fast,it will generate non-uniform microstructure formation of steel plates,and hydrogen-induced-cracking sensitivity is increased.

Thus, the invention provides anti-hydrogen-induced-cracking pressurevessel steel and a manufacturing method thereof. Theanti-hydrogen-induced-cracking pressure vessel steel is suitable forbeing used in wet H2S environment, composition design and productionprocess are simple, and it is suitable for mass production, and nopatent related to the technology have been found through research.

SUMMARY OF THE INVENTION

The invention aims to solve current technical issues mentioned in theprior art, and provides a type of manufacturing method to produceSA516Gr70(HIC) steel plate with 50 mm thickness, which can be used toproduce petrochemical devices, those are able to be applied in a wet H2Scorrosive environment. The steel plate has high strength, and goodimpact toughness at low temperature, and low hardness, and high anti-HICperformance. The steel plate has fine grain size and less non-metallicinclusion content without obvious banded structure. After long-timehigh-temperature simulated post-welding heat treatment, the strength andlow temperature impact toughness of the steel plate are not reducedobviously, and the steel plate for head end can meet the manufacturingrequirements of both cold forming and hot forming processes at the sametime.

The technical scheme of the invention is to solve the above problems: atype of Pressure Vessel Steels for Resistance to Hydrogen-InducedCracking, chemical composition of the steel plate according to theweight percentage of C:0.16˜0.20%, Si:0.15˜0.40%, Mn:1.05˜1.20%,P=0.008%, S=0.002%, Nb:=0.01%, V=0.01%. Ti:=0.01%, B=0.0005%: balance ofFe and unavoidable impurities, carbon equivalent Ceq less than 0.42%,the carbon equivalent formula:

Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15.

The performance of Resistance to Hydrogen-Induced Cracking of pressurevessel steel plate is that: Resistance to Hydrogen-Induced Cracking testis conducted on the steel plate according to NACE TM0284-2011“Experimental method for evaluating Resistance to Hydrogen-InducedCracking performance of pressure vessel steel plate”, use solution A todo validation: crack length ratio (CLR), crack thickness ratio (CTR) andcrack sensitivity ratio (CSR) of a single inspection section are allequal to 0, and no hydrogen blister is observed, in other words, nodefect is observed after corrosion. After simulated post-welding heattreatment at 635±14° C. for 18 h, the yield strength of the steel plateis greater than or equal to 360 Mpa, tensile strength is greater than orequal to 540 Mpa, and transverse Charpy impact energy single value isgreater than or equal to 150 J; Brinell hardness of the steel platesurface at delivery-state is less than or equal to 170 HB, the grade ofgranularity is greater than or equal to grade 8.0, and the grade ofbanded structure is less than or equal to grade 2.0.

The chemical contents of Pressure Vessel Steels for Resistance toHydrogen-Induced Cracking (HIC) with 50 mm thickness are determined inthe way as specified in the description.

The main chemical of the steel plate is the combination of C, Si and Mn,the content of S and P is reduced as much as possible, alloy elementslike Cr, Ni, Cu, Mo, Nb, V, Ti and B are not added intentionally. Thecomposition design is simple. Carbon element can remarkably improve thestrength and hardness of the steel plate; But with the increase ofcarbon content, carbide segregation is prone to occur easily, resultingin the hardness of the segregation zone different from the hardness ofits surrounding microstructure, leading to HIC corrosion. Mn element canimprove the strength of the steel plate through solution strengthening;however, when Mn higher than 1.05%, cracking sensitivity can beincreased. but the adverse effect can be eliminated throughintercritical quenching and tempering. Silicon is mainly used asreducing agent and deoxidizer in steelmaking, and has certain solidsolution strengthening effect; meanwhile, Si element can be easilysegregated in grain boundary, and promote intergranular crackgeneration. With the increase of C, Mn and Si content, the sensitivityof HIC will be increased, but as the major strengthening elements, thecontents should be controlled close to upper limits in the allowablerange. The control range of the application is C:0.16˜0.20%,Si:0.15˜0.40%, Mn:1.05˜1.20%, and the adverse effects are eliminated bysubsequent heat treatment. P and S are harmful elements. With thecontent of S increases in the steel, the amount of hydrogen enteringsteel when steel is soaked in H2S increases too, resulting in thesensitivity of HIC is also increased. When the P content is very low,cracks is nucleated at MnS, but cannot be detected due to small size.However, if the content of P is high (for example, P=0.4%), crack isnucleated and propagates at oxide inclusions and grain boundary even atthe condition when the content of S is very low (for example, S=0.001%).Therefore, it is necessary to reduce the content of S and P in steel asmuch as possible in this application.

Cracks can nucleate and extend on oxide inclusion and grain boundary.

The invention also aims to provide a manufacturing method of theanti-hydrogen-induced-cracking pressure vessel steel plate, as follows:

(1) Smelting Process

Continuous casting slab is adopted for production with using processroute: KR pretreatment→converter smelting process smelting→LFrefining→RH refining→continuous casting. Improving purity of moltensteel and reduction of slab segregation are the essential measures forresistance to hydrogen-induced cracking of steel. Smelting raw materialare pretreated by KR process. Slag-off treatment is conducted afterconverter smelting process, the content of S is strictly controlled tobe less than or equal to 0.001% and P is less than or equal to 0.006%.Non-metallic inclusions of Class A, class B, class C, class D and classDs in single level is less than or equal to 1, the total sum is lessthan or equal to 3.5;

Continuous casting with low superheat and full argon protection isadopted. Through dynamic soft pressing technology, the segregation ofthe casting slab is controlled under level 1 of class B, and the slab iscooled down for more than 48 hours after the slab is formed, in this wayit can ensure the full diffusion of hydrogen in the steel.

(2) Heating and Rolling Process

A sectional heating method is adopted, total heating time is 225-300min, the temperature of a first heating section is 1050-1150° C., thetemperature of second heating section is 1200-1260° C., the temperatureof soaking section is 1170-1250° C., the total heating time of thesecond heating section together with soaking section is longer than orequal to 120 min, the second heating section and the soaking section arematched to promote sufficient hydrogen diffusion, segregation diffusionand formation of uniform microstructure.

A two-stage rolling technology is adopted, the high-temperaturelarge-reduction rolling technology is adopted in rough rolling stage. Inthe longitudinal rolling passes, there are at least two passes withsingle-pass rolling reduction greater than or equal to 50 mm; theaccumulated reduction ratio of the finish rolling stage is larger thanor equal to 60%, finish rolling temperature is controlled to be 780-820°C., ACC is applied after rolling, and steel plates are stacked andslowly cooled for over 72 h after produced from production line, so thatsufficient hydrogen diffusion can be realized.

(3) Heat Treatment Technology

The subcritical quenching and tempering technology is adopted, heatingtemperature during subcritical quenching is Ac1-Ac3, quenchingtemperature is 820-850° C., soaking time factor is 1.8-2.0 min/mm, andwater cooling is conducted; in order to prevent the steel plate strengthfrom greatly decreasing after simulated post-welding heat treatment,steel plate tempering temperature is not lower than simulatedpost-welding heat treatment temperature, tempering temperature is640-670° C., and soaking time factor is 3.5-4.5 min/mm.

Subcritical quenching can reduce brittle transition temperature andrefine grains, so that a proper number of evenly distributed fineferritic structures can be obtained, crack extension can be inhibited,and steel toughness can be improved remarkably. Compared to conventionalquenching technologies, it requires lower tempering temperature toobtain the steel with equal harness, and with higher toughness, torestrain the stress concentration and hinder the crack initiation andpropagation; the presence of non molten ferrite in the quenchedstructure leads to increase the content of carbon and alloy elements inaustenite. After quenching, a small amount of stable retained austenitecan also prevent the initiation and propagation of cracks. Subcriticalquenching can also reduce the segregation of harmful impurity elementsat austenite grain boundary, then it can purify the grain boundary.

Compared with the prior art, the advantages of this invention arefollowing:

Our invention relates to the SA516Gr70 CHIC)anti-hydrogen-induced-cracking (HIC) pressure vessel steel plate with 50mm thickness. The steel plate has high strength, and good impacttoughness at low temperature, and low hardness, and high anti-HICperformance. The steel plate has fine grain size and less non-metallicinclusion content without obvious banded structure. After long-timehigh-temperature simulated post-welding heat treatment, the strength andlow temperature impact toughness of the steel plate are not reducedobviously. For the fabrication of pressure vessels, the head is producedby using cold forming process, due to the fact that work hardening canincrease the hardness of steel plate, easily lead to cracking of steelplate. The delivery-state hardness of the steel plate is controlledbelow 170 HB, it can still meet the requirement on cold working afterwork hardening. Therefore, the steel plate produced by this method canmeet the requirements both on cold forming and hot forming processes forhead forming process.

In order to achieve the above purpose, the continuous casting process isadopted to reduce the hydrogen induced cracking sensitivity by reducingthe segregation of the slab, improving the purity of the molten steel,and reducing the banded structure of the steel plate.

The composition design of the steel plate is simple, the major elementsof the steel plate are C, Si and Mn alloy, alloy elements like Ni, Cr,Cu, Mo, Nb, V and Ti are not added intentionally, the design can reducesegregation with low production cost. And the hydrogen-induced crackingsensitivity of the steel plate is reduced by reducing the content ofelements S, P, H, 0 and N, and by improving the purity of molten steel.

Casting blanks are heated with step heating mode, particularly, thetotal time of the second heating segment and the soaking zone isprolonged, so that segregation diffusion can be achieved sufficiently;by means of the high-temperature large-reduction rolling technology inthe high-temperature rolling stage, loose defect can be sufficientlypressed, so that the internal quality of steel plate can be improved.

The unique subcritical quenching and tempering technology is adopted forheat treatment of the steel plate. Compared with the quenchingtechnology and the normalizing technology, heating temperature forsubcritical quenching is low, the cooling rate of the cooling processduring subcritical quenching is between normalizing temperature andquenching, and strength-toughness properties in steel can be optimizedafter further high-temperature tempering; in this way, the tensilestrength and the low temperature impact toughness of the steel plate canbe improved. At the same time, the high surface hardness of steel platecan be avoided, the structure of the steel plate is ferrite and pearlitestructure, grain size is small without obvious banded structure exists.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a metallurgical structure of a steel plateaccording to embodiment 1 of the invention;

FIG. 2 is a diagram of a metallurgical structure of a steel plateaccording to embodiment 2 of the invention;

FIG. 3 is a diagram of a metallurgical structure of a steel plateaccording to embodiment 3 of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Further explanation is made on the invention with reference to thedrawings and embodiments.

Embodiment 1

The thickness of the anti-hydrogen-induced-cracking steel plate forpressure vessel is 50 mm. Its chemical composition is determined byweight percentage: 0.17% of C, 0.34% of Si, 1.18% of Mn, 0.004% of P,0.0005% of S, 0.00006% of H, 0.0015% of 0, 0.0035% of N, and the balancebeing Fe and inevitable impurity elements. Carbon equivalent Ceq is lessthan or equal to 0.41%, and the computational formula for the carbonequivalent is

Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15.

The manufacturing process of the steel plate is as follows:

(1) Smelting and Continuous Casting

Continuous casting slabs which have 370 mm in thickness are adopted forproduction, smelting materials are subjected to KR molten steelpretreatment, converter smelting, LF refining, RH refining and plateslab continuous casting in sequence, Slag-off treatment is conductedafter converter steel making, low-superheat pouring with whole-courseargon protection is adopted for continuous casting, casting blanksegregation is controlled by means of the dynamic soft-reductiontechnology, and plate slabs are covered and slowly cooled for over 48 hafter exiting the line.

(2) Heating and Rolling Technologies

A segmented heating method is adopted, total heating time is 270 min,the temperature of a first heating segment is 1120° C., the temperatureof a second heating segment is 1250° C., the temperature of a soakingzone is 1240° C., the total heating time of the second heating segmentand the soaking zone is 135 min, and sufficient diffusion of castingblank segregation is ensured.

A two-stage rolling technology is adopted, the high-temperaturelarge-reduction rolling technology is adopted in the rough rollingstage, and there are three longitudinal rolling passes with single-passrolling reduction being 25 mm, 55 mm and 50 mm respectively; porousdefect can be sufficiently pressed, so that the internal quality and thecore performance of the steel plate can be improved. The accumulatedreduction ratio of the finish rolling stage is 65%, finish rollingtemperature is controlled to be 810° C., ACC fast cooling is appliedafter rolling, and steel plates are stacked and slowly cooled for over72 h after steel plates come out of production line.

(3) Heat Treatment Technology

The subcritical quenching and tempering technology is adopted, Ac1temperature of the steel plate is 720° C., Ac3 temperature is 850° C.,quenching temperature is 835° C., and soaking time factor is 1.8 min/mm;tempering temperature is 660° C., and soaking time factor is 3.8 min/mm.

The 50 mm thick anti-hydrogen-induced cracking pressure vessel steelplate manufactured with the method has well-matched comprehensivemechanical properties and excellent anti-hydrogen-induced-crackingperformance, the mechanical properties are shown in Table 1, theanti-hydrogen-induced-cracking performance is shown in Table 4, and thephoto of the metallographic structure is shown in FIG. 1.

Embodiment 2

The thickness of the anti-hydrogen-induced-cracking steel plate forpressure vessel is 50 mm. Its chemical composition is determined byweight percentage: 0.18% of C, 0.32% of Si, 1.17% of Mn, 0.003% of P,0.0006% of S, 0.00005% of H, 0.0012% of 0, 0.0036% of N, and the balancebeing Fe and inevitable impurity elements. Carbon equivalent Ceq is lessthan or equal to 0.41%, and the computational formula for the carbonequivalent is

Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15.

The manufacturing process of the steel plate is as follows:

(1) Smelting and Continuous Casting

Continuous casting slabs which are 370 mm in thickness are adopted forproduction, smelting materials are subjected to KR=pretreatment,converter smelting, LF refining, RH refining and plate slab continuouscasting in sequence, slag off treatment is conducted after convertersteel making, low-superheat pouring with whole-course argon protectionis adopted for continuous casting, casting blank segregation iscontrolled by means of the dynamic soft-reduction technology, and plateslabs are covered and slowly cooled for over 48 h after steel platescome out of production line.

(2) Heating and Rolling Technologies

A segmented heating method is adopted, total heating time is 285 min,the temperature of a first heating segment is 1125° C., the temperatureof a second heating segment is 1255° C., the temperature of a soakingzone is 1242° C., the total heating time of the second heating segmentand the soaking zone is 150 min, and sufficient diffusion of castingblank segregation is ensured.

a two-stage rolling technology is adopted, the high-temperaturelarge-reduction rolling technology is adopted in the rough rollingstage, and there are three longitudinal rolling passes with single-passrolling reduction being 25 mm, 55 mm and 55 mm respectively; porousdefect can be sufficiently pressed, so that the internal quality and thecore performance of the steel plate can be improved. The accumulatedreduction ratio of the finish rolling stage is 66%, finish rollingtemperature is controlled to be 812° C., ACC=is applied after rolling,and steel plates are stacked and slowly cooled for over 72 h afterexiting the line.

(3) Heat Treatment Technology

The subcritical quenching and tempering technology is adopted, whereinthe subcritical quenching has a quenching temperature of 842° C. andsoaking time factor of 1.8 min/mm; the tempering has a temperingtemperature of 650° C. and soaking time factor of 4.0 min/mm.

The 50 mm thick anti-hydrogen-induced-cracking pressure vessel steelplate manufactured with the method has well-matched comprehensivemechanical properties and excellent anti-hydrogen-induced-crackingperformance, the mechanical properties are shown in Table 2, theanti-hydrogen-induced-cracking performance is shown in Table 4, and thephoto of the metallographic structure is shown in FIG. 2.

Embodiment 3

The thickness of the anti-hydrogen-induced-cracking steel plate forpressure vessel is 50 mm. Its chemical composition is determined byweight percentage: 0.16% of C, 0.35% of Si, 1.16% of Mn, 0.005% of P,0.0007% of S, 0.00006% of H, 0.0012% of 0, 0.0033% of N, and the balancebeing Fe and inevitable impurity elements; carbon equivalent Ceq is lessthan or equal to 0.40%, and the computational formula for the carbonequivalent is

Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15.

The manufacturing process of the steel plate is as follows:

(1) Smelting and Continuous Casting

Continuous casting slabs are adopted for production, smelting materialsare subjected to KR pretreatment, converter smelting, LF refining, RHrefining and plate slab continuous casting in sequence, slag offtreatment is conducted after converter steel making, low-superheatpouring with whole-course argon protection is adopted for continuouscasting, casting blank segregation is controlled by means of the dynamicsoft-reduction technology, and plate slabs are covered and slowly cooledfor over 48 h after steel plates come out of production line.

(2) Heating and Rolling Technologies

A segmented heating method is adopted, total heating time is 300 min,the temperature of a first heating segment is 1118° C., the temperatureof a second heating segment is 1252° C., the temperature of a soakingzone is 1241° C., the total heating time of the second heating segmentand the soaking zone is 150 min, and sufficient diffusion of castingblank segregation is ensured.

A two-stage rolling technology is adopted, the high-temperature largereduction rolling technology is adopted in the rough rolling stage, andthere are three longitudinal rolling passes with single-pass rollingreduction being 30 mm, 55 mm and 55 mm respectively; porous defect canbe sufficiently pressed, so that the internal quality and the coreperformance of the steel plate can be improved. The accumulatedreduction ratio of the finish rolling stage is 68%, finish rollingtemperature is controlled to be 802° C., ACC fast cooling is appliedafter rolling, and steel plates are stacked and slowly cooled for over72 h after exiting the line.

(3) Heat Treatment Technology

The subcritical quenching and tempering technology is adopted, and thesubcritical quenching has a quenching temperature of 840° C. and soakingtime factor of 1.8 min/mm; the tempering has a tempering temperature of645° C. and soaking time factor of 4.2 min/mm.

The 50 mm thick anti-hydrogen-induced-cracking pressure vessel steelplate manufactured with the method has well-matched comprehensivemechanical properties and excellent anti-hydrogen-induced-crackingperformance, the mechanical properties are shown in Table 3, theanti-hydrogen-induced-cracking performance is shown in Table 4, and thephoto of the metallographic structure is shown in FIG. 3.

TABLE 1 Mechanical properties of steel plate produced in embodiment 1Surface Charpy impact energy Thick- Yield Tensile Elonga- BrinellTemper- ness Sampling Sample strength strength tion hardness, atureEmbodiment mm position direction Sample state MPa MPa % HB ° C. Impactenergy 1 50 ½ horizontal subcritical quenching + 382 560 32 168 −51 187196 205 thickness tempering subcritical quenching + 365 542 35 152 −51162 174 186 tempering + simulated thermal forming + simulatedsubcritical quenching + simulated tempering + simulated post-weldingheat treatment subcritical quenching + 371 551 33 160 −51 182 186 198tempering + simulated post-welding heat treatment Note: simulatedthermal forming: 920+/−20° C., 1.1-1.2 min/mm, water cooling; simulatedpost-welding heat treatment: 635+/−14° C. × 18 h. The simulatedsubcritical quenching and simulated tempering technology have the sameparameters with the steel plate thermal treatment technology.

TABLE 2 Mechanical properties of steel plate produced in embodiment 2Surface Charpy impact energy Thick- Yield Tensile Elonga- BrinellTemper- ness, Sampling Sample strength, strength, tion hardness, ature,Embodiment mm position direction Sample state MPa MPa % HB ° C. Impactenergy 2 50 ½ horizontal subcritical quenching + 385 564 32 169 −51 185193 200 thickness tempering subcritical quenching + 362 544 36 155 −51172 184 182 tempering + simulated thermal forming + simulatedsubcritical quenching + simulated tempering + simulated post-weldingheat treatment subcritical quenching + 375 550 34 161 −51 188 184 192tempering + simulated post-welding heat treatment Note: simulatedthermal forming: 920+/−20° C., 1.1-1.2 min/mm, water cooling; simulatedpost-welding heat treatment: 635+/−14° C. × 18 h. The simulatedsubcritical quenching and simulated tempering technology have the sameparameters with the steel plate thermal treatment technology.

TABLE 3 Mechanical properties of steel plate produced in embodiment 3Surface Charpy impact energy Thick- Yield Tensile Elonga- BrinellTemper- ness, Sampling Sample strength, strength, tion hardness, ature,Embodiment mm position direction Sample state MPa MPa % HB ° C. Impactenergy 1 50 ½ horizontal subcritical quenching + 380 558 31 165 −51 197195 215 thickness tempering subcritical quenching + 364 546 36 150 −51168 176 196 tempering + simulated thermal forming + simulatedsubcritical quenching + simulated tempering + simulated post-weldingheat treatment subcritical quenching + 375 550 34 162 −51 192 188 194tempering + simulated post-welding heat treatment Note: simulatedthermal forming: 920+/−20° C., 1.1-1.2 min/mm, water cooling; simulatedpost-welding heat treatment: 635+/−14° C. × 18 h. The simulatedsubcritical quenching and simulated tempering technology have the sameparameters with the steel plate thermal treatment technology.

TABLE 4 Anti hydrogen-induced cracking (HIC) performance of steel platesproduced in all embodiments Section 1 Section 2 Section 3 HydrogenSample CSR CLR CTR CSR CLR CLR CTR CSR CLR blister Embodiment No. % % %% % % % % % (HB) 1 sample 1 0 0 0 0 0 0 0 0 0 nil sample 2 0 0 0 0 0 0 00 0 nil sample 3 0 0 0 0 0 0 0 0 0 nil 2 sample 1 0 0 0 0 0 0 0 0 0 nilsample 2 0 0 0 0 0 0 0 0 0 nil sample 3 0 0 0 0 0 0 0 0 0 nil 3 sample 10 0 0 0 0 0 0 0 0 nil sample 2 0 0 0 0 0 0 0 0 0 nil sample 3 0 0 0 0 00 0 0 0 nil

The granularity of the steel plates in all embodiments is grade 8.5, thebanded structure is grade 0.5, as shown in FIG. 1-FIG. 3.

1. An anti-hydrogen-induced-cracking pressure vessel steel plate,characterized by comprising, chemical composition of the steel plateaccording to the weight percentage: 0.16-0.20% of C, 0.15-0.40% of Si,1.05-1.20% of Mn, less than or equal to 0.008% of P, less than or equalto 0.002% of S, less than or equal to 0.01% of Nb, less than or equal to0.01% of V, less than or equal to 0.01% of Ti, less than or equal to0.0005% of B, and the balance being Fe and inevitable impurity elements;carbon equivalent Ceq is less than or equal to 0.42%, and the formulafor calculating the carbon equivalent isCeq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15; wherein theanti-hydrogen-induced-cracking pressure vessel steel plate is made bythe following steps: (1) smelting technology continuous casting slabsare adopted for production with following process route of KRpretreatment, converter smelting, LF refining, RH refining, continuouscasting, smelting materials are pretreated with KR molten steel,slag-off treatment is conducted after converter steel making, thecontent of S is strictly controlled to be less than or equal to 0.001%and P less than or equal to 0.006%, each of Group A, Group B, Group C,Group D and Group Ds nonmetallic inclusions has a chart diagram index ofless than or equal to 1.0, and their sum is less than or equal to 3.5;low-superheat pouring with whole-course argon protection is adopted forcontinuous casting, casting slab segregation B is controlled to be undergrade 1.0 by means of the dynamic soft-reduction technology, and plateslabs are covered and slowly cooled for over 48 h after exiting theline, so that hydrogen in steel can diffuse sufficiently; (2) heatingand rolling technologies a segmented heating method is adopted, totalheating time is 225-300 min, the temperature of a first heating segmentis 1050-1150° C., the temperature of a second heating segment is1200-1260° C., the temperature of a soaking zone is 1170-1250° C., andthe total heating time of the second heating segment and the soakingzone is longer than or equal to 120 min; a two-stage rolling technologyis adopted, the high-temperature large-reduction rolling technology isadopted in the rough rolling stage, and there are at least twolongitudinal rolling passes with single-pass rolling reduction greaterthan or equal to 50 mm; the accumulated reduction ratio of the finishrolling stage is greater than or equal to 60%, finish rollingtemperature is controlled between 780 and 820° C., ACC fast cooling isapplied after rolling, and steel plates are stacked and slowly cooledfor over 72 h after come out of production line, so that sufficienthydrogen diffusion can be realized; (3) heat treatment technology thesubcritical quenching and tempering technology is adopted, wherein thesubcritical quenching has a quenching temperature of 820-850° C. andsoaking time factor of 1.8-2.0 min/mm, after that water cooling isconducted; and then tempering, wherein the tempering has a temperingtemperature of 640-670° C. and soaking time factor of 3.5-4.5 min/mm.